1. Technical Field
The present invention relates to single or multiple layer composite pet pads which include at least one layer formed from a mixture of thermoplastic and other nonthermoplastic fibers, such as wood pulp fibers and an insecticide.
2. Description Of The Prior Art
Articles and materials formed of a combination of thermoplastic and other fibers, such as wood pulp fibers, are known. However, these prior articles suffer from a number of disadvantages and are not known to comprise pet pads which include insecticides.
U.S. Pat. No. 4,458,042 of Espy discloses an absorbent material comprised of a consolidated blend consisting essentially of wood pulp fluff and wetting agent treated spurted polyolefin pulp. Representative polymers for the spurted polyolefin pulps include polyethylene, polypropylene and copolymers of ethylene and propylene. Mixtures of two or more of these polymers are also described as a suitable polyolefin pulp. The polyolefin pulp and wood pulp are blended, formed into a fluff pad and then consolidated by heating to a temperature above the melting point of the polyolefin pulp.
Although useful, absorbent materials formed in this manner tend to lose fibers from their outer edges, particularly when shaken. In addition, pads of these consolidated materials have a relatively low Z direction tensile strength which makes them relatively easy to pull apart, especially at the peripheral edges and by a pet. Also, pads of these materials do not impede the leakage of urine or other liquids deposited on these materials from their outer edges. Furthermore, Espy does not have or suggest the inclusion of insecticides for killing fleas, lice, mites and other pests.
U.S. Pat. No. 4,609,580 of Rockett et al. discloses an absorbent floor mat comprising a combination of a nonwoven liquid permeable wear surface, such as of nylon, an absorbent coform inner layer of a mixture of polymeric microfibers and wood pulp, and a liquid impervious film backing layer. Intermittent bonds within the periphery or field of the floor mat are provided. These bonds are formed by a patterned application of sonic energy or heat and pressure.
The absorbent layer of Rockett et al. is stated to have a basis weight in the range of from about 100-500 g/m.sup.2 and preferably in the range of about 150-250 g/m.sup.2. The absorbent layer is described in this patent as preferably being formed in accordance with the "coform" process described in U.S. Pat. No. 4,100,324 of Anderson et al. In the Anderson coform approach, streams of molten polymer are deposited in an airstream and combined by a secondary air stream containing, for example, wood pulp fibers. A combination of the air streams causes the distribution of the wood pulp in the microfiber matrix. Staple fibers, such as polyester, polyolefins, polyamides and mixtures thereof, can also be included. Finally, the liquid impermeable surface is described as preferably being a film with examples being thermoplastic polymers such as polyolefins, polyesters and the like, including polyethylene or polypropylene films. The film is described as being applied as a separate layer, coextruded, or coated onto the absorbent web. Calendering the exposed absorbent surface or providing a bottom adhesive layer are described as alternate ways of achieving liquid imperviousness of the underside of the floor mat.
In forming an absorbent layer in the manner of U.S. Pat. No. 4,100,324 of Anderson et al., the meltblown microfibers are softened, but are not above their melting point when they are engaged by wood pulp or the "other" fibers. Consequently, the bonding that occurs between these microfibers and the "other" fibers is relatively weak in comparison to the bonding that results when a thermobonding approach is used. Thermobonding in this sense means raising the temperature of a mixture of thermoplastic and other fibers to a temperature which is above a melt point of at least one of the thermoplastic fibers in the mixture. When this happens, a much stronger fusing of the mixture results. This makes the pad more resistant to tearing by a pet. In addition, by relying on field bonds to secure the floor mat together, the Z direction tensile strength of the Rockett et al. composite mat is relatively weak. Moreover, the peripheral edges of the Rockett et al. floor mat are as weak as the interior areas of the mat and would not impede the leakage of liquid from these edges. In addition, Rockett et al. does not suggest the inclusion of an insecticide for pest control.
Another example of a pad which exemplifies the prior art is described in U.S. Pat. No. 4,650,481 of O'Connor et al. The pad of O'Connor et al. has a liquid impermeable backing sheet, an overlaying liquid permeable face sheet and an absorbent coform layer between the backing and face sheets. The interior of the pad is provided with a quilted pattern of compression lines described as being formed by ultrasonic bonding, heat and compression or the use of glue and compression. In an illustrated example, the pad is generally rectangular and the quilting lines appear to form a pattern of squares on the pad. The backing sheet is described as being generally bonded to the absorbent material by adhesive.
The coform absorbent material of the O'Connor et al. patent is described as being of meltable polymers and staple fibers formed as disclosed in U.S. Pat. No. 4,100,324 of Anderson et al. Typical polymers are described as polyethylene, polyesters, nylon and other thermoplastic fibers. Staple fibers are described as including cotton, polyester, rayon, and nylon. A combination of polypropylene meltblown fibers and wood pulp fibers is described as preferred in any desired ratio, but preferably with meltblown polypropylene fibers being present in an amount from between about 30% and about 40% by weight of the mixture. Examples of the backing sheet in O'Connor et al. include polymer films, such as copolymers of ethylene and vinyl acetate, nylon and polyesters. The preferred backing sheet films are identified in this patent as being of polyethylene or polypropylene and a composite of polypropylene and a lightweight spun bonded fabric. Spunbonded polypropylene is listed in this patent as one example of a facing sheet.
During one method of manufacturing the O'Connor, et al. pad, the facing sheet is placed on a foraminous belt with meltblown polypropylene and wood fibers being deposited onto the facing sheet as it moves below meltblown producing nozzles. The coform thus becomes mechanically attached to the facing sheet. The combined coform and facing sheet is brought in contact with an adhesively coated polymer backing sheet which is secured to the coform side of the combination. The pad is then embossed to form the quilting pattern.
The O'Connor et al. patent suffers from many of the drawbacks of the Rockett et al. floor mat discussed above. For example, coform provides relatively weak bonding of a pad. In addition, there is a tendency of the pad of O'Connor et al. to leak at the edges. O'Connor, et al. recognizes this and describes an embodiment (FIGS. 6 and 7) directed toward solving this problem. In this embodiment, the absorbent material is centered but does not extend completely to the peripheral edge of the pad. Instead, the facing and backing sheets are directly connected at the edge of the pad. Moreover, O'Connor does not suggest the inclusion of an insecticide in such a pad.
Therefore, although thermoplastic fibers have been combined with other fibers and used in the manufacture of articles, a need exists for improved materials and articles of this type and for pet pads of such materials which include an insecticide.